Fertilization happens when a sperm fuses with the female act during sexual intercourse and further forms an egg that gets implanted in the uterus of the female. The sperm goes through the fallopian tube and penetrates the zona pellucida layer of the ovum (female egg) and then fuses with it which forms a zygote (fertilized egg). Thousand of sperms are generated in a male body to compensate for the ones unfit and non-motile ones. Once the zygote is created or formed, it gets implanted in the uterus and further growth starts taking place when cells start dividing and forming tissues, and tissues further form organs which result in the formation of an organ system, eventually or in time turning into an organism.